Ammonium nitrate explosive



Patented July 1, 1952 AMMONIUM NITRATE EXPLOSIVE James A. Farr, Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington, Del., a corporation of Delaware H No Drawing. Application February 26, 1948,

- Serial No. 11,330

4 Claims.

. 1 This application relates to explosive compositions.

An object of the invention is the provision of ammonium nitrate explosive compositions of rates or velocities of detonation of improved stability.

. Another object of the invention is the provision of ammonium nitrate explosives of decreased setting tendency.

A further object of the invention is the provision of ammonium nitrate explosives resistant to alteration by temperature changes.

Other objects of the invention will be apparent from the following description.

For. many years ammonium nitrate has been employed as the principal power producing ingredient of many commercial explosives. Since by itself ammonium nitrate is not ordinarily considered sufiiciently sensitive for explosive purposes, sensitizing ingredients are applied to ammonium nitrate in the production of practical explosives. A common and advantageous class of sensitizers is that of the explosive liquid nitric esters, of which nitroglycerine alone, or mixed with nitro sugars or nitroglycols, is the most com mon example.

The velocity of detonation of ammonium nitrate explosives may be varied to a considerable extent by alteration in the grain size of the ammonium nitrate employed. To obtain some useful velocities, particularly in the lower ranges, ammonium nitrate of relatively large grain size is employed.

Coarse grained ammonium nitrate explosives sensitized with explosive liquid nitric esters have, however, in the past been subject to at least three rather serious disadvantages:

1. They have tended to set on standing into hard masses which become quite insensitive and difficult to handle;

2. The have tended to rise considerably in detonation velocity on being subjected to fluctuating summer temperatures; and

.3. They have sometimes tended to show increased velocity when detonated under confinement as compared with their velocity when detonated in the open.

Since explosives are ordinarily employed under conditions of confinement and are usually stored under outdoor temperature conditions, these velocity jump phenomena have been particularly objectionable.

It has been found in accordance with the present invention that coarse grained ammonium nitrate sensitized with explosive liquid nitric ester produces explosives of highly stable detonation velocity characteristics and of much decreased setting tendency when potassium nitrate is included in solid solution throughout the ammonium nitrate grain. With granular ammonium nitrate explosives of this type, the velocity jump on confinement is usually greatly minimized, and the velocity change on temperature fluctuation is usually practically eliminated.

Granular ammonium nitrate for explosive use is generally prepared by evaporating solutions of ammonium nitrate nearly to dryness and then cooling the molten mass under agitation, as in a graining kettle or a continuous crystallizer. As the ammonium nitrate cools it crystallizes and gives 01f heat of crystallization which evaporates the remaining water. The grain size and hardness obtained is controlled by the amount of evaporation prior to crystallization, and also by the addition of small quantities of grain modifying salts, such as ammonium chloride and ammonium sulphate. Grain modifying salts are usually added either in the evaporating equipment or to the graining equipment prior to the addition of the molten ammonium nitrate.

While ammonium nitrate for explosive use is also sometimes produced by cracking castings, the stability improvements eifected by the present invention are chiefly noted with material, the grains of which are produced directly from a melt.

The potassium nitrate employed in accordance with the present invention may be added to the ammonium nitrate in any manner which distributes it in complete solution. For example it may be added directly to the molten ammonium nitrate, or it may be added to the crystallizing equipment prior to introduction of the ammonium nitrate therein.

Also since ammonium nitrate solutions are usually formed by neutralizing an ammonia solution with nitric acid, the potassium nitrate ammonium nitrate mixture may be prepared in situ by nitric acid neutralization of a mixture of ammonia and potassium hydroxide or carbonate.

The amount of potassium nitrate included in solid solution in ammonium nitrate in accordance with the present invention may be varied somewhat depending upon the extent of stabilizing effect and other properties desired in the finished explosive.

Metal nitrates, of which potassium nitrate and. sodium nitrate are common and well known examples, are often employed as ingredients of ammonium nitrate explosives. These salts find particular use for oxygen balance adjustment and for control of flame characteristics. The potassium nitrate employed in solid solution with ammonium nitrate in accordance with the present invention may replace metal nitrate which would otherwise be employed as an ingredient of the explosive mix.

Since in some explosives large quantities of metal nitrate are not desired, and in view of cost considerations, it is sometimes desired to limit the quantity of potassium nitrate employed in accordance with the present invention. It will be usually found that considerable stabilizing effect over a fairly wide range of temperature fluctuation is still obtained when amounts of potassium nitrate as low as about 4% by weight ofthe ammonium nitrate are employed in accordance with the present invention. On the other hand, amounts of potassium nitrate above about 7.5% of the ammonium nitrate do not usually materially aid in increasing the stabilizing, and antisetting effects obtained by the invention, and amounts above about 11% of the ammonium nitrate will often be found undesirable. Ammonium nitrate containing about 6.5% of potassium nitrate is often about optimum for purposes of the present invention.

The present invention finds application chiefly with coarse grained ammonium nitrates. It appears to be only ammonium nitrate of the coarser grain sizes which produces velocity jumps on temperature fluctuation. Usually the invention will be found to have a diminished application when the ammonium nitrate is of a grain size such that less than about 70% is held on all. S. S. No. 70 screen.

Since ordinarily the ammonium nitrate used in explosives passes a U. S. S. No. 8 screen, the invention will not generally be applied to ammonium nitrate of a grain size coarser than this.

Explosive liquid nitric esters, such as nitroglycerine, with which the ammonium nitrate of the invention is sensitized, have, of course, a detonation velocity of their own. Explosives containing large amounts of explosive liquid nitric ester usually approach the velocity of the ester. Since the applicability of the present invention lies largely in the stabilization of the ammonium nitrate, it will be found that the invention has a diminished utility with explosives having high explosive liquid nitric ester contents. However, the effectiveness of the invention is usually retained to considerable degree in explosives containing as high as about of explosive liquid nitric ester. On the other hand contents below about 3% of explosive liquid nitric ester do not usually give sufficient sensitizing effects for commercial explosives.

The invention will be further described by the following examples which illustrate specific embodiments:

EXAMPLE 1 An aqueous solution containing a solids content of 92.7% ammonium nitrate, 6% potassium nitrate (about 6.5% based on ammonium nitrate), 1% ammonium chloride, and 0.3% ammonium sulphate was evaporated until it had a crystallization temperature (fudging point) of about 308 F. The molten mass was then run into a jacketed crystallizing kettle where it was cooledwith agitation until a dry grained material resulted. The grained product was screened through a U. S. S. No. 8 screen, and the small residue of lump material was discarded. Not more than 2% of the material produced passed a U. S. S. No. 70 screen.

EXAMPLES 2 THROUGH 7 Several explosive compositions were made up in conventional dynamite mixers and were packed in 1%" by 8 paper cartridges. The detonation velocities of some of these cartridges were determined in the open and when confined by tamping into 1 /2 diameter, open-ended, steel pipe. Other of the cartridges were then cycled by heating them to 117 F. for 7 hoursand cooling to about 40 F. for 16- hours. The confined detonation velocities of the cycled cartridges were then measured. Confined detonation velocities were also determined after a similar Second and third cycle. The composition of the powders and the velocities obtained are tabulated below.

Table I Example- Nitroglycerine percent 8. 8.80 8.80 6.0 6. 0 6.0 Coarse Ammonium Nitrate Percent 81. 20 76.20 80.4 80. 4 Coarse Potassium Ammonium Nitrate Percent (Product of Example 1) 81.20 85. 4 Fine Ammonium Nitrate Percent 2. 50 2. 50 2. 50 Sodium Nitrate Percent". 5. 0 Potassium Nitrate Percent. 5.00 5.0 Yellow Corn Flour Percent 4.75 4.75 4.75 2.0 2.0 2.0 Fine Apricot Pit Pulp Percent 4. 1 4. 1 4.1 Wood Pulp Per cent 2. 25 2. 25 2. 25 2.0 2. 0 2.0 Chalk Perccnt. 0.50 0.50 0. 50 0.5 0.5 0.5 Cartridges/5M... 94.1 94. 7 92. 7 96.0 98.1 95. 7 Open Velocity (it./scc.) 7,000 6,800 6,800 5,400 5,300 5,400 Confined Velocity:

As made (ft/soc.) 7, 600 7,600 7,700 5,900 5, 600 5, 900 1 cycle (it/sec) 7, 600 8, 800 6. 900 5, 300 7,700 2 cycles (ft/sec.) 5, 800 8, 700 3 cycles (ft/sec.) 5,800 9, 500

It will be noted that the powder made with mixed grain potassium and ammonium nitrate (Examples 3 and 6) in each case showed a stability to cycling. The powder made without potassium nitrate (Examples 1 and 5) or with potassium nitrate merely in mechanical admixture (Examples 4 and 7) jumped in Velocity on cycling.

EXAMPLES 8 THROUGH 10 To show the effects of varying amounts of potassium nitrate in solid solution in ammonium nitrate, preparations of ammonium. nitrate similar to those of Example 1 but containing about 4.75% and about 10% of potassium nitrate, based on ammonium nitrate, were made. These materials were made up into powder and tested for detonation velocity as in Examples 2 through 7, except that cycling tests for Example 8 were made between 117 F. and 65 F. and also between 117 F. and 8 F., and the cycling. tests for Examples 8 and 9 were made between 117 F. and 8 F. The formulae and results are tabulated below:

Fine Apricot Pit Pulp percent Chalk percent Cartridges/50# Open Velocity (ft./sec.) Confined Velocity:

As made 1 cycle (117 F565 F.) 2 cycles (117 F.65 F.) 3 cycles (117 F.65 F. 1 cycle (117 F.-8 F.) 2 cycles (117 F.8 F.) 3 cycles (117 F.8 F.) 8,700 7, 500

It will be seen from Example 8 that the small amount (4.5%) of potassium nitrate was sufficient to stabilize velocity on cycling between 117 F. and 65 F. but was not sufficient to prevent a velocity rise when cycling was conducted between 117 F. and 8 F. On the other hand, it may be seen from Examples 9 and 10 that the larger amount of potassium nitrate (10%) was sufficient to stabilize against velocity increase even for the more drastic cycling between 117 F. and 8 F.

EXAIVIPLES 11 AND 12 To show the eifect of potassium nitrate-ammonium nitrate solid solutions for stabilizing the velocity of powder made up with a higher percentage of nitroglycerine, the powders tabulated below were made up and tested. The cycling tests were conducted between 117 F. and 40 F., and the potassium ammonium nitrate was made in accordance with the method of Example 1.

Table III Example earnestnessare;1;1:11; 3:31.11?

Coarse Potassium Ammonium Nitrate Per cent (Product of Example 1) Fine Apricot Pit pulp Per cent Bagasse Per cent Wood Pulp Per cent Chalk Per cent- Cartridges/50# Open Velocity (ft/sec.) Confined Velocity:

As made on m Ingr m... o o czooooonzo can COO coo cycles 10, 300

ules consisting of a solid solution comprising ammonium nitrate and from about 4 to about 11 based on ammonium nitrate, of potassium nitrate uniformly distributed throughout their structure, said crystallized granules being of a size such as to pass a U. S. S. No. 8 screen and be held to the extent of at least about on a U. S. S. No. 70 screen, and said crystallized granules being sensitized with up to about 20% of an explosive liquid nitric ester.

3. An explosive comprising crystallized granules consisting of a solid solution comprising am monium nitrate and from about 4% to about 11% of potassium nitrate uniformly distributed throughout their structure, said crystallized granules being of a size such as to pass a U. S. S. No. 8 screen and be held to the extent of at least about 70% on a U. S. S. No. 70 screen, and said crystallized granules being sensitized with from about 3% to about 20% of an explosive liquid nitric ester.

4. An explosive according to claim 3 in which the content of potassium nitrate in solid solution with said ammonium nitrate in said crystallized granules is about 6.5%.

JAMES A. FARR.

REFERENCES CITED The following references are of record in the 7 OTHER REFERENCES Bebie, Manual of Explosives, Military Pyrotechnics and Chemical Warfare Agents, published 1943 by MacMillan 8: Company, New York, pages 25 and 26. 

3. AN EXPLOSIVE COMPRISING CRYSTALLIZED GRANULES CONSISTING OF A SOLID SOLUTION COMPRISING AMMONIUM NITRATE AND FROM ABOUT 4% TO ABOUT 11% OF POTASSIUM NITRATE UNIFORMLY DISTRIBUTED THROUGHOUT THEIR STRUCTURE, SAID CRYSTALLIZED GRANULES BEING OF A SIZE SUCH AS TO PASS A U. S. S. NO. 8 SCREEN AND BE HELD TO THE EXTENT OF AT LEAST ABOUT 70% ON A U. S. S. NO. 70 SCREEN, AND SAID CRYSTALLIZED GRANULES BEING SENSITIZED WITH FROM ABOUT 3% TO ABOUT 20% OF AN EXPLOSIVE LIQUID NITRIC ESTER. 